Gold plating has been widely used in recent years in electronic equipment and electronic components, particularly to protect the connection terminal surface of electronic components because the gold has excellent electrical properties, corrosion resistance, and the like. Gold plating is also used as the surface treatment of the electrode terminals of semiconductor elements and as the surface treatment of electronic components such as connectors to connect electronic equipment. The electronic components, such as connectors, are generally made of copper or copper alloys. In order to usually apply gold plating on these electronic components, the nickel plating is applied at first on the copper surface as base plating, followed by gold plating on the nickel plating layer. However, since gold is an expensive noble metal, the thickness of the gold plating film is reduced as much as possible to use a smaller amount of gold and to reduce the manufacturing cost when manufacturing these electronic components.
However, the number of pinholes in the gold plating film increases with decreasing gold plating film thickness. These pinholes cause problems such as corrosion of underlying metal nickel and base metal copper, raise the contact resistance by deposition of the corrosion reaction product on the surface, and the like if water, chlorides, and other such corrosive substances penetrate the pinholes.
Sealing treatment is one of the methods to solve this problem. The sealing treatment is a surface treatment for gold to improve corrosion resistance by covering pinholes by the action of chemicals on the surface of the gold plating film. Japanese laid-open patent publication No. 9-170096 describes a sealing treatment solution containing an inhibitor and a self-emulsifier, and Japanese laid-open patent publication No. 2003-129257 describes a water-based sealing agent containing an inhibitor, a surfactant, and an amine compound. In these documents, benzotriazole and the like are exemplified as inhibitor, and during sealing treatment, DC electrolysis is carried out by using the plating material as anode. However, for the method of performing electrolysis in the sealing treatment, additional equipment is required for sealing treatment. On the other hand, the present inventors conducted studies and found that when an aqueous solution containing benzotriazole as the sealing agent is used and DC electrolysis is not performed, the sealing of the pinholes is not enough, thus corrosion may occur. Therefore, it has been desired to develop a sealing agent highly capable of sealing pinholes with a simple treatment method without performing electrolysis.